A known image scanner turns off a light source and detects outside light in a state where an open-close type document cover is open for reducing an influence of outside light that enters from the outside of the apparatus.
An image input device emits light of red, green, and blue from a light source to one line of an original document in a main scanning direction, converts reflection light of that light into electric signals to read an image, then turns off the light source to read one line, and performs arithmetic processing on the both read data, thereby reducing the influence of outside light.